Microbial Pattern Recognition and Signaling by the Adhesion GPCR BAI1

摘要 先天性免疫系统是机体抵抗微生物入侵的第一道防线 病原体固有免疫应答的组成部分是模式识别受体（PRR），其 识别由广泛的病原微生物表达的保守决定簇。其中 是Toll样受体，其促进炎症信号传导和吞噬细胞募集，以响应 病原体识别，以及介导微生物吞噬清除的吞噬PRR的几个家族 感染的组织。每个受体家族都包含多个成员，它们识别一个独特的光谱， 微生物组分，并且它们共同提供针对广泛的感染性生物体的保护。 我们已经确定了一种新的模式识别受体，BAI 1，它特异性地识别表面 革兰氏阴性菌的脂多糖（LPS）。BAI 1是一个知之甚少的G家族的成员， 蛋白偶联受体（GPCR），即所谓的粘附GPCR。细菌与BAI 1的结合触发了它们的 宿主吞噬细胞的快速内化和杀伤，通过一种涉及激活小细胞的机制， 通过埃尔莫/Dock GEF复合物直接与BAI 1相互作用。是否以及如何发出信号 通过异源三聚体G蛋白被整合到这个过程是未知的，将是Aim 1的重点。 先天免疫中的一个新兴主题是，模式识别受体通常与每个 另一个用于增强下游信号响应。我们公布的和初步的数据表明，BAI 1的行为， 与Toll样受体TLR 4串联，以促进活性氧（ROS）的产生， 吞噬细胞，以及炎性细胞因子/趋化因子/干扰素亚群的合成， 表达由转录因子IRF 3介导。在目标2中，我们将确定如何从 BAI 1影响TLR 4介导的信号转导，以驱动ROS产生和促炎因子的转录 基因. 这项研究的最终目的是确定BAI 1在宿主防御中的作用， 细菌感染在目标3中，我们将描述BAI 1缺陷的巨噬细胞和中性粒细胞的能力， 在革兰氏阴性腹膜炎的小鼠模型中明确感染。BAI 1驱动ROS产生的能力， 还将测定感染期间特定骨髓细胞亚群中细胞因子/干扰素的合成。一起 这些研究将提供独特的生物化学和生理学的见解，以一类新的模式识别 在对细菌病原体的先天免疫应答中具有重要功能的受体。此外，BAI 1是一个 已知生理配体的少数粘附GPCR，以及对其信号传导特性的剖析将 揭示了对这类知之甚少的受体的新见解。

Abstract The innate immune system forms the first line of specific host defense against invading microbial pathogens. Integral to the innate immune response are Pattern Recognition Receptors (PRRs), which recognize conserved determinants expressed by a broad range of pathogenic microorganisms. Among these are the Toll-like receptors, which promote inflammatory signaling and phagocyte recruitment in response to pathogen recognition, and several families of phagocytic PRRs that mediate phagocytic clearance of microbes from infected tissues. Each receptor family contains multiple members that recognize a unique spectrum of microbial components, and collectively they provide protection against a wide range of infectious organisms. We have identified a novel pattern recognition receptor, BAI1, that specifically recognizes the surface lipopolysaccharide (LPS) of Gram-negative bacteria. BAI1 is a member of a poorly understood family of G- protein coupled receptors (GPCRs), the so-called Adhesion GPCRs. Binding of bacteria to BAI1 triggers their rapid internalization and killing by host phagocytes, through a mechanism involving activation of the small GTPase Rac by the Elmo/Dock GEF complex, which interacts directly with BAI1. Whether and how signaling through heterotrimeric G proteins is integrated into this process is not known, and will be the focus of Aim 1. An emerging theme in innate immunity is that pattern recognition receptors often cooperate with each other to enhance downstream signaling responses. Our published and preliminary data indicate that BAI1 acts in tandem with the Toll-like receptor TLR4 to promote the production of reactive oxygen species (ROS) by phagocytic cells, and the synthesis of a subset of inflammatory cytokines/chemokines/interferons whose expression is mediated by the transcription factor IRF3. In Aim 2 we will determine how signals derived from BAI1 influence TLR4-mediated signaling to drive ROS production and the transcription of pro-inflammatory genes. The ultimate goal of the proposed research is to define the role of BAI1 in host defense against bacterial infection. In Aim 3, we will characterize the ability of BAI1-deficient macrophages and neutrophils to clear infection in a mouse model of Gram-negative peritonitis. The ability of BAI1 to drive ROS production and cytokine/interferon synthesis in specific myeloid cell subsets during infection will also be determined. Together these studies will provide unique biochemical and physiological insights into a new class of pattern recognition receptor with important functions in the innate immune response to bacterial pathogens. Moreover, BAI1 is one of the few Adhesion GPCRs with known physiological ligands, and dissection of its signaling properties will reveal new insights into this poorly understood class of receptors.